Radiographic imaging such as x-ray imaging has been used for years in medical applications and for non-destructive testing.
Normally, an x-ray imaging system includes an x-ray source and an x-ray detector system. The x-ray source emits x-rays, which pass through a subject or object to be imaged and are then registered by the x-ray detector system. Since some materials absorb a larger fraction of the x-rays than others, an image is formed of the subject or object.
It may be useful to begin with a brief overview of an illustrative overall x-ray imaging system, with reference to FIG. 10. In this non-limiting example, the x-ray imaging system 10 basically comprises an x-ray source 11, an x-ray detector 12 and an associated image processing device 15. In general, the x-ray detector 12 is configured for registering radiation from the x-ray source 11 that may have been focused by optional x-ray optics and passed an object or subject or part thereof. The x-ray detector 12 is connectable to the image processing device 15 via suitable analog processing and read-out electronics (which may be integrated in the x-ray detector or detector system 12) to enable image processing and/or image reconstruction by the image processing device 15. An example of a commonly used x-ray imaging system is a Computed Tomography (CT) system, which may include an x-ray source that produces a fan or cone beam of x-rays and an opposing x-ray detector or detector system for registering the fraction of x-rays that are transmitted through a patient or object. The x-ray source and detector system are normally mounted in a gantry that rotates around the imaged object.
Development in the CT field makes increasingly high gantry rotation speeds and higher spatial resolution of the detectors possible; with this, the requirement for sufficient angular sampling increases. Insufficient angular sampling in CT leads to aliasing which destroys the reconstructed images by introducing streak-like artifacts from sharp edges. Several approaches for oversampling in CT, such as flying focal-spot (FFS) and quarter detector offset (QDO), have been developed, and are predominantly used standard methods, in order to decrease the risk of aliasing. Both the number of samples and the grid on which the sinogram is sampled determine the risk for aliasing.